1. Field of the Invention
The present invention relates generally to the optical imaging field and, more particularly, to an actuator and an auto-focus imaging system using the actuator.
2. Description of Related Art
Auto-focus techniques have been widely employed in various imaging systems, including still camera systems and video camera systems. Nowadays there are basically two main auto-focus methods: one is an active focus (i.e., distance metering) method, and the other is a passive focus (i.e., focus detection) method. In particular, the passive focus method mainly employs a charge-coupled device (CCD) and works by evaluating the amount of contrast or the phase difference in a scene. The active focus method usually uses an infrared light or ultrasound emitter and a corresponding receiver in a triangular surveying system, the data thus generated being converted by a microprocessor (e.g., a well-known digital signal processor) into information about distance and thereby enabling the automatic focusing by an auto-focus imaging system.
Generally, a digital auto-focus camera system includes an optical imaging assembly, an image sensor, a control unit, and an actuator. The optical imaging assembly usually includes a movable lens assembly. The image sensor can be a CCD or a complementary metal oxide semiconductor device (CMOS). The control unit can be, for example, a digital signal processor or an image signal processor. The actuator commonly includes a stepper motor and a drive circuitry. The drive circuitry, regulated by the control unit, can drive the stepper motor to perform a rotational movement. In order to carry out the position adjustment of the movable lens assembly in an automatic focusing process, a gear assembly has necessarily been employed in the lens movement system to transform the rotational movement of the stepper motor into linear movement. However, the existence of the gear assembly generally renders the lens positioning system unduly bulky. Furthermore, the occurrence of backlash/recoil in the gear assembly will usually result in a degraded focusing accuracy.
It is therefore desirable to find a new actuator and a new auto-focus imaging system, which can overcome the above mentioned problems.